1. Field of the Invention
This invention relates to the monitoring of water quality and the detection of trace dissolved organic compounds, leached plasticizers, and/or carbon (DOCs) in water and drinking water.
2. Description of the Prior Art
Most approaches for monitoring water quality in water processing plants are based on “wet” chemistry techniques that require the addition of other chemicals to water samples. Many use gas chromatography or liquid chromatography followed by laser fluorescence detection in a reagent capillary tube, while others use reagents that change pH, color, or other physical characteristics depending upon the concentration of selected or trace species. Although useful in the lab, these techniques work less well in the field, where reagents are difficult to replace and harsh conditions may degrade them.
Earlier laser-induced fluorescence (LIF) studies of water have used either blue-green (513.5 nm) argon ion lasers or doubled (535 nm) Nd:YAG lasers for excitation, as well as staining reagents for improving the contrast of detected organisms. Studies that have relied on natural or auto-fluorescence from water have generally not been as successful as those that have used fluorescent dyes. This is perhaps because blue-green wavelengths do not sufficiently separate between the emission spectral peaks due to trace organics versus excitation or interfering background spectra.
As a result, few previous LIF studies have drawn on the natural fluorescence of trace species in the water. The novel system therefore employs a deep-UV laser source near 220 nm-300 nm for excitation to overcome some of the limitations of the natural fluorescence approach. The resultant fluorescence emission from the organics is well separated from the excitation wavelength.
There is a need for a reagentless, deep UV (220 nm-300 nm) laser-induced-fluorescence (LIF) system for detecting contaminates and potentially harmful substances in bottled and processed water and the ocean.
It is known that expensive laser-based fluorescence detection of dissolved organic compounds in drinking water is feasible. Previous work by the inventors has shown that laser induced fluorescence can be used for the detection of trace DOCs and leached plasticizers (such as Bisphenol-A) in water and that different drinking water samples from different bottled water manufacturers show significant different levels of DOCs and/or plasticizers. Such prior art work appears in several research publications such as: (1) Tunable ultraviolet laser-induced fluorescence detection of trace plastics and dissolved organic compounds in water, Vasanthi Sivaprakasam and Dennis K. Killinger, Applied Optics 42, 6739 (2003), (2) Development and initial calibration of a portable laser induced fluorescence system used for in situ measurements of trace plastics and organics in seawater and the Gulf of Mexico, Vasanthi Sivaprakasam, Robert Shannon, Caiyan Luo, Paula G. Coble, Jennifer Boehme, and Dennis K. Killinger, Applied Optics 42, 6747 (2003), and (3) Water Monitoring with Laser Fluorescence, Dennis Killinger and Vasanthi Sivaprakasam, Invited Review, OSA Optics and Photonics News, p 35, January 2006
The 266 nm UV laser used for excitation in these published prior art studies by the authors and inventors cost $10,000. Accordingly, there is a need for a low cost, compact LED to replace the known expensive lasers.
Currently, no real time or reagentless laser-induced-fluorescence systems have been authorized for use by water treatment plants. However, for the past several years, some water agencies have been testing a selected range of UV absorption and fluorescence water monitoring instruments. One such device is a UV-visible (200 nm-750 nm) absorption instrument from S-CAN in Austria that can detect small changes in the optical absorption properties of water.
Another fluorescence-based test is used to monitor water for the e-coli bacteria. This involves growing a culture obtained from a water sample, using a fluorescence dye or stain, and counting the organisms by either visual microscopes or laser readers. Fluorescence is also used in liquid chromatography laser-induced fluorescence, or LC-LIF, a technique in which a capillary tube is used to separate the chemical species and a laser reads the separated column.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the identified needs could be met.